(1) Field of the Invention
The present invention relates to a sound field expanding device whereby a sound field formed by two loudspeakers can be expanded to an arbitrarily wide angle, and natural and clear sound images can be obtained.
(2) Description of the Prior Art
When a two channel stereo sound signal is supplied directly to speakers arranged at an oblique angle in front of a listener, the reproduced sound field is restricted between the speakers without regard to the range of the original sound field picked up by the microphones of the recording apparatus.
In addition, if the angle subtended between the speakers is narrower than the original angle substended between the microphones, the reproduced sound field is deformed more narrowly than the original sound field.
Accordingly, it is desired to expand the reproduced sound field so that it will be much greater than the angle subtended between the speakers.
Hitherto, in expanding a sound field formed by a stereo sound signal derived from a conventional two or four channel stereo sound signal source; for instance, from a conventional stereo sound disc, one method of expanding the sound field has been adopted such that crosstalk components having adequate phase or time differences are added respectively to both left and right channel sound signals L and R composing the stereo sound signal. However a defect remains in this method in that localized directions of sound images in the expanded sound field are very obscure, and a remarkably unnatural aural feeling is caused by the out-phase sounds.
On the other hand, by using another sound field expanding method proposed previously, it is required that sound signals to be reproduced are picked up by plural microphones with respectively specified level and phase differences from sound sources. Therefore, it is difficult to apply the proposed method for the purpose of expanding a sound field formed by sound signals derived from a conventional sound disc. Furthermore, in order to reproduce a fairly wide sound field by the above-proposed method, it is necessary to use the same number, at least five, sound image localizing devices as the number of sound sources portions of which should be localized in the reproduced sound field. Therefore, it is expensive to realize a sound field expanded by the above-proposed method.